Atomic scale friction properties of confined water layers

Abstract

The atomic scale friction properties of water layers are a highly important subject for understanding the lubricating mechanism of ice. Recently, two-dimensional (2D) materials gave rise to an excellent platform for investigating the tribological properties of water, since water layers can be easily intercalated between 2D layers and hydrophilic substrates. In this Review, we highlight recent research on the friction properties of the confined water between hydrophilic (mica and silica) substrates and 2D materials. Recent friction force microscopy work has revealed the nanotribological properties of water intercalated between 2D materials (e.g., graphene and MoS2), and a hydrophilic substrate increases the friction force. Moreover, the friction on both graphene and MoS2 increased as the number of stacking water layers increased. On the other hand, the magnitude of friction increase went down as the number of covering 2D layers above the intercalated water layer increased; the friction is eventually indistinguishable from the multilayer stack excluded water adsorption. The isotope effect of frictional enhancement has been addressed, and it was shown that the intercalation of deuterium oxide (D2O) leads to the decrease of friction at H2O intercalated graphene on mica due to the lower vibrational frequency of D2O adsorbate, which is associated with the low rate of frictional energy dissipation at the interface. Water exfoliated by 2D layers prepared with mechanical exfoliation and chemical vapor deposition exhibits similar frictional enhancement, indicating the universal tendency of friction by intercalated water between 2D atomic layers and hydrophilic surfaces.

Direct Observation of Atomic-Scale Gliding on Hydrophilic Surfaces

“…Two-dimensional (2D) materials, such as atomically thin graphene, have been widely utilized as model systems for understanding friction phenomena, due to crystallinity, flexibility, rigidity, and other characteristics. − Therefore, studies have been conducted to understand the origins of water-involved friction phenomena on graphene-deposited HS. For example, the contribution of flexural phonon modes of graphene on mica, which is generated by water layer interaction, was confirmed by experimental and theoretical works after exposure to high RH of graphene on mica. , The ice-like water layer at the interface between two-dimensional atomic layers (including graphene and MoS 2 ) and hydrophilic surface acts as an antilubricant. , The isotope effect, arising from ordinary and heavy (deuterium oxide) water treatments, was attributed to different vibrational frequencies of water molecules governing frictional energy dissipation . However, the frictional effect of water on HS during exposure to high RH conditions has not been addressed.…”

“…For example, the contribution of flexural phonon modes of graphene on mica, which is generated by water layer interaction, was confirmed by experimental and theoretical works after exposure to high RH of graphene on mica. 24,31 The ice-like water layer at the interface between two-dimensional atomic layers (including graphene and MoS 2 ) and hydrophilic surface acts as an antilubricant. 32,33 The isotope effect, arising from ordinary and heavy (deuterium oxide) water treatments, was attributed to different vibrational frequencies of water molecules governing frictional energy dissipation.…”

Phase‐dependent Friction on Exfoliated Transition Metal Dichalcogenides Atomic Layers

“…However, in strongly adherent and atomically flat mica due to its high surface energy, there was little or no observed friction difference with respect to layer thickness. [34]…”

Nanoscale friction characteristics of layered-structure materials in dry and wet environments

“…The friction of graphene is influenced by the flow of water molecules, which is affected by their arrangement in the vicinity of the surface (Neek-Amal et al, 2016). Ordering of water molecules has been observed adjacent to 2D layers (Lee et al, 2019;Go et al, 2021). MD simulations have provided insight into the contribution of ordered water layers (hydration layers) to the origin of stick-slip behavior of few-layer graphene (Vilhena et al, 2016).…”